Thursday, February 22, 2007

I'm Stabby McSpear! Put Me in Your Tasty Bushbabies!

There's an exceptionally cool article in Current Biology's "Online Ahead of issue" section this week by Jill Preutz from Iowa State University and Paco Bertolani who seems to be a graduate student at Cambridge. In it, they report that chimpanzees in their study communities routinely make spears for use in hunting. It's a well-written article, and it's chock full of novel observations with far-reaching implications. The following is rated S for Stabby.

Primate tool use is taken somewhat for granted these days, but it's worth remembering that Jane Goodall's initial reports of termite fishing and wadge dipping at Gombe were met with considerable skepticism fewer than 50 years ago. And just when we'd gotten comfortable with our closest relatives modifying the environment through nonbiological means, there was the revelation in the mid-1990s that orangutans (the most distant of our Great Ape relatives) also made and used tools in the wild. Gorillas would join the party even later in late 2005. The bonobos, to date, remain on the outside looking in, possibly because their tools are sex-toy oriented and therefore not much good for opening doors.

So our thinking on tool use has come a long way just in the last few years. We've gone from thinking that a culture-ready brain (or at least a technology-ready one) evolved just 7 million years or so ago (before the human-Pan split) to accepting that, neurologically, the right stuff has been with the Hominoid lineage for more than twice as long. We've also realized that a number of different social structures, ranging from the semisolitary orangutan to the gregarious, constantly shifting community of the chimpanzee, can result in tool-using individuals. We've also had to give up overly simplistic notions about handedness and language going, as it were, hand-in-hand. Hell, just last week we had to give up any last-ditch hopes that chimpanzees might somehow have "caught" tool use from humans.

Even though chimpanzee tool use is, comparatively, a pair of comfy old cognitive pajamas, this research by Preutz and Bertolani introduces some pinholes here and there as well as a few things that might constitute a previously unrecognized pajamial butt flap. First off, the context of tool use is new and exciting: At Fongoli (the Senegalese study community), the chimps use tools for hunting, which has a couple of new and exciting implications.

A less radical, but still interesting, factor about the hunting context is the preferred prey of the Fongoli chimps. Elsewhere, chimpanzees tend to hunt young baboons, colobus monkeys of all ages, and things like antelope and bush pigs. At Fongoli, the environment is considerably drier than that of other chimps and these preferred prey are absent. The Fongoli chimps hunt bushbabies (a small, nocturnal prosimian primate) instead, using their spears to stab into the hollows where they shelter as they sleep the day away. Several characteristics of Fongoli hunting are probably related to this choice of prey.

First of all, the small size of the bushbaby, combined with its nocturnal activity patterns, mean that a lone chimp has a greater chance of success, whereas larger diurnal prey might be out of reach for the solitary hunter. An individual who successfully captures and kills a bushbaby thus has no social obligation to share the meat (elsewhere, hunted meat is virtually the only resource that is shared among adult chimps who parcel out the spoils to the hunters and to females who . . . ahem . . . have something to offer). The small size of the kill also probably contributes to the solo consumption. The "shooting fish in a barrel" (seriously, could you bring yourself to stab this in its sleep?) nature of bushbaby hunting also opens this economic niche to individuals who don't usually hunt, namely subadults and females.

The real kicker about the context of Fongoli tool use, though, is the fact that ape tool use in hunting is pretty much novel. Up until now, all food-related tool use by chimps has taken place in foraging contexts: They open nuts with stone or wood hammers; they make leaf sponges and dip for water; they dip stalks and twigs into ant or termite mounds and fish them out. Although "rousing" use of tools has been observed in isolated cases elsewhere, the Fongoli chimps employ tools in hunting frequently.

In addition to the quantitative shift from rare to routine, there's a qualitative difference: Whereas a chimp at Mahale picked up a nearby branch to rouse a squirrel from a hole, the Fongoli chimps are using spears to stab at the prey repeatedly. It is not yet clear whether or not the prey is killed (or even injured) with the spear, but there's a cognitively important difference between using a branch merely to extend the length of the arm and using a spear as a weapon. This isn't just appealing to those of us who enjoy a spot of violence now and again, it is very likely to improve the chimp's success by allowing him or her to invade the busbaby's nest and immobilize the prey in one swift movement. Rousing use of tools is just as likely to give the prey time to escape.

So tool use in an entirely new context is cool. New prey is conceptually cool for humans, albeit bad news for the endangered Senegalese bushbaby. Experimentation with hunting by chycks and youngsters also on the well-chilled end of the news spectrum. New data on chimpanzee cognitive evident in how they use their tools, approaching absolute zero.

But the real seat-busting potential of this research is in the manufacture of the tools themselves. Certainly there is something about the image of chimps running around with spears that tingles the Alan Moore sensors of the brain all on its own, but the data on the modification process certainly have more than just the "Stabby Chimps = Crazy Awesome" street value. Preutz and Bertolani characterize the manufacture of spears by the Fongoli chimps as "crafting," which doesn't sound like an earth shaking declaration. In anthropological circles, where even today we insist that the object in use be an "unattached environmental object" (this criterion was used for long time to deny the title of tool use to behaviors like "bridging" among male orangutans who bend saplings to travel from one larger trunk to the other), crafting has a flatbed of baggage with it.

The process that the chimps use to create their spears is both hierarchical and flexible. Certain steps must be taken early on, regardless of formal aspects of the material or any other factors, but once the base modifications are complete, the chimps can and do alter their techniques on the fly. That speaks volumes about their ability to generalize, which we consider to be an especially important facet of human intelligence. Another aspect of the manufacture that is especially intriguing is the fact that the chimps are sharpening the end of the tool using their teeth.

Again, this is a qualitative shift in a behavior that is seen in other contexts. In termite and ant dipping, as well as in nut-meat extraction (shut up JRH, a chimp will often use teeth to break off the tool after it is chosen and to strip it of leaves. However, in those contexts, the tool cannot fit into the space without the modification. At Fongoli, the sharpening behavior is not simply to make the tool fit, it is part and parcel of how the chimp wishes to use the tool. My favorite sentence in the entire article: "Chimpanzees forcibly ‘‘jabbed’’ (sensu Marlowe [16])." As I said earlier to M and J, it is now my goal to see in print "[Organism foo] comprehensively dismembered (sensu Matilda) that punkass po po bitch."

In terms of the bigger picture, the context of Fongoli tool use has real potential to shift our view of the early hominid resource base. As much as we have always loved a "Man the Hunter" model for our own evolution, most of the evidence suggests that hunting and tool use have fuck all to do with our first divergence from the Pan lineage. The earliest hominids do not have the teeth of a habitual meat eater, in terms of either architecture or wear; the earliest tools are persistently linked to scavenging/foraging behaviors (extracting marrow from the sloppy seconds of large carnivores and/or extracting insects from bark and mounds); and there's not a lot of clear evidence linking the earliest bipeds to any kind of tools at all.

The Fongoli chimps represent routine and systematic attempts at hunting with tools that are nondurable. Although there is the potential to do archaeological research into how long this behavior has been in their repertoire, ancient hominid behaviors of this type will be archaeologically invisible (at least until we shift our framework for recovering and recognizing tool-using behaviors) because of the much greater time elapsed. Thus, although it remains pretty incontrovertible that hunting and meat eating were not an appreciable trick up the hominid sleeve (not that we had sleeves until much later) until the emergence of Homo erectus about 2 million years ago, it is possible that hominids began experimenting with tool-assisted hunting as well as foraging at a much earlier date.

Off the top of my oversized head, I think that conceptual nugget has the potential to shed light on how the frilly heck we made it out of Africa in such a hurry, as the evidence from Dmanisi and tool finds in China suggest (both emphasize mastery of hunting as a key factor). I also wonder if there are dental implications for the chimps that would shed light on the weird dental problems that plagued the Neanderthals. To be sure, the Neanderthals had a wide variety of stone tools they could have used for sharpening, but it's also been suggested that a cognitive barrier prevented them from envisioning the snazzy, hafted, multicomponent tools that those rockstar modern humans favored.